A multimedia broadcast/multicast service (hereinafter, referred to as “MBMS”) is to provide a streaming or background service to a plurality of user equipments by using a downlink dedicated MBMS bearer service. In a network, an MBMS bearer uses a point-to-multipoint wireless bearer service or a point-to-point wireless bearer service.
The MBMS is divided into a broadcast mode and a multicast mode. The MBMS broadcast mode is a service for transmitting multimedia data to all user equipments (UEs) within a broadcast area. The broadcast area refers to a region where the broadcast service is possible. On the other hand, the MBMS multicast mode is a service for transmitting the multimedia data to a specific user equipment group only within a multicast area. The multicast area refers to a region where the multicast service is possible.
A procedure of providing a specific MBMS from a network to a user equipment by using a multicast mode will be described below. First of all, user equipments which desire to receive the MBMS should undergo a subscription procedure. Subscription refers to establishing a relationship between a service provider and a user equipment. Also, the user equipments which desire to receive the MBMS should receive a service announcement provided by the network. The service announcement refers to providing the user equipments with a list of services to be provided and related information of the services.
Meanwhile, a user equipment which desires to receive the MBMS of the multicast mode should join a multicast group specifically. The multicast group refers to a group of user equipments which receive a specific multicast service, and joining refers to merging with a multicast group to receive the specific multicast service. The user equipment can notify the network through the above joining that it desires to receive specific multicast data. On the other hand, the user equipment which has joined the multicast group can unsubscribe to joining of the multicast group, which is referred to as leaving.
Each user equipment performs the subscription, joining and leaving procedures. The user equipment can perform the subscription, joining, and leaving procedures at any time, such as before data transmission, during the data transmission, or after the data transmission.
The MBMS can be divided into a multi-cell service and a single cell service, wherein the multi-cell service is to provide a service to a plurality of cells, and the single cell service is to provide a service to a single cell. The multi-cell service provides the service through a multicast channel (MCH), and the single cell service provides the service through a downlink shared channel (DL SCH). If the user equipment receives the multi-cell service through the MCH, the user equipment can receive the same multi-cell service transmitted from various cells by combining in an MBMS single frequency network (MBSFN) mode.
To provide the MBMS, the network provides MBMS control channel (MCCH) and MBMS traffic channel (MTCH). The MCCH is used to transmit control information for MBMS transmission to the user equipment while the MTCH is used to transmit the MBMS to the user equipment. The MBMS is comprised of one or more sessions, wherein only one session can exist during one time interval.